Valve spring retainers are used in internal combustion engines to operatively retain a return spring on the stem of a poppet valve. Self-locking valve spring retainers are known in the art wherein the retainer automatically locks on the stem of the poppet valve as the retainer is pressed onto the valve stem. Self-locking valve spring retainers are advantageous in that they are easily installed in one quick motion by pressing onto the valve stem.
Examples of self-locking valve spring retainers may be had in U.S. Pat. No. 4,879,978 to Pierce, the inventor of the subject invention, issued Nov. 14, 1989, U.S. Pat. No. 3,273,856 to Tauschek, issued Sep. 20, 1966, and U.S. Pat. No. 3,612,016 to Jeken, issued Oct. 12, 1971. These references all disclose self-locking valve spring retainers for operatively retaining a return spring on the stem of a poppet valve. All three of the references disclose an annular base ring, which in Tauschek is discontinuous, and a plurality of arms extending in cantilever fashion from the base ring for flexing as the retainer is pressed over the end of the valve stem to an operative position. A self-locking means extends from each of the flexible arms for automatically engaging and gripping the valve stem when in the operative position.
However, the prior art is deficient in that as the retainer is pressed over the end of the valve stem with the arms flexing prior to engagement of the self-locking means on the valve stem, significant stresses are created in the base ring which leads to cracking and premature failure, especially in cold weather due to the increased brittleness of the retainer. Also, such damaging stresses in the base ring will prevent the retainer from being reused if ever removed for servicing reasons. Also, the valve spring retainers of the prior art are deficient in that the self-locking means includes only one locking step per arm for engaging and interlocking with a single mating projection of the valve stem. Hence, all of the shear stresses between the valve stem and the retainer are transferred through one locking step per arm.
Additionally, the self-locking valve spring retainers are difficult to remove from the valve stem because the force of the return spring causes the retainer to more tightly clamp onto the poppet valve stem. Hence, any effort to flex the arms outwardly to disengage the self-locking means becomes a battle against the return spring instead of simply against the elasticity of the retainer.